It is widely known that voltage converting devices are used in power generation for providing an output voltage to a grid or to a supplying network. Such a voltage converting device comprises voltage converting units which are arranged e.g. in parallel electrical connection to one another. The voltage converting units are electrically connected to a plurality of interphase transforming units each of which may comprise a primary coil and a secondary coil being magnetically coupled to one another via a magnetic core member.
In order to control or adapt the switching frequencies of the voltage converting units to one another, a pulse width modulation (PWM) control apparatus may be provided which outputs a control signal for each one of the voltage converting units. Further, the PWM control apparatus may be used for balancing magnetizing currents of the interphase transforming units, in order to allow for an improved operation of the voltage converting device.
WO 2008/030919 A2 discloses a voltage converting device which comprises three voltage converting units being in parallel electrical connection to one another. Each of the voltage converting units is electrically connected to a different one of three interphase transforming units, wherein each of the interphase transforming units comprises a primary coil and a secondary coil which are magnetically coupled to one another via a magnetic core member. In order to enable a phase shift of the voltage outputted by the voltage converting units and a balancing of the magnetizing currents of the interphase transforming units, a PWM control apparatus is provided which enables one of the voltage converting units acting as a master for the other two voltage converting units with respect to the load current. A feedback control signal to the two “slave” voltage converting units is based on a difference current obtained by a difference between the current of the “master” voltage converting unit and the current of a different one of the “slave” voltage converting units. Therefore, a balancing of the currents of the slave voltage converting units compared to the current of the master voltage converting unit is provided.
U.S. Pat. No. 4,802,079 discloses a PWM control apparatus for a voltage converting device. The voltage converting device comprises two voltage converting units being in parallel electrical connection to one another and two interphase transforming units each of which comprises one coil. The current provided by the voltage converting units are summed up and compared to a total reference current. Further, the currents provided by the voltage converting units are subtracted, in order to obtain the difference current. The summed currents and the difference current are combined in terms of signal adding and signal subtraction, and each of the two combination currents are compared to a reference signal before feeding signal back to the voltage converting units.